<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>A-盒模型</title>

    <style>
        /*.demo{*/
            /*width: 100px;*/
            /*height: 100px;*/
            /*border: 1px solid #ddd;*/

            /*border-top-right-radius:8px;*/
            /*border-bottom-left-radius:8px;*/
        /*}*/

        .demo{
            width:100px;
            height:100px;
            background:#000;
            color:#fff;
            padding:10px;
            border:5px solid red;
            box-sizing:content-box;
        }

    </style>

</head>
<body>
<div class="demo">
    CSS3 学习分享
</div>

</body>
</html>